1. Field of Invention
The present invention relates to electro-optical devices, such as liquid crystal devices and electronic apparatuses. The present invention also relates to an electrophoresis device, such as an electronic paper, an EL (electroluminescent) device, and a device using an electron emission element (a field emission display and a surface-conduction electron-emitter display).
2. Description of Related Art
In the related art, an electro-optical device, such as a liquid crystal device capable of displaying an image, in which an electro-optical material, such as liquid crystal is interposed between a pair of substrates and light is transmitted so as to pass through the substrates and the electro-optical material, is disclosed. “Displaying the image”, for example, is realized by changing the state of an electro-optical material in each pixel to change the transmittance ratio of light and by causing light with different gray scales to be sensed in each pixel.
Such an electro-optical device is active-matrix driven by including, on one of the pair of substrates, pixel electrodes arranged in a matrix, scanning lines and data lines positioned to thread through the pixel electrodes, and TFTs (thin film transistors) as pixel switching elements. In the electro-optical device capable of being active-matrix driven, the TFTs are provided to control conduction between the pixel electrodes and the data lines. Further, the TFTs are electrically connected to the scanning lines and the data lines. Therefore, it is possible to control the on or off of the TFTs through the scanning lines and to apply image signals received through the data lines to the pixel electrodes. For example, to change the transmittance ratio of light in each pixel when the TFTs are turned on.
In the above-mentioned electro-optical device, the above-mentioned various components are formed on one substrate. However, when the components are expanded two-dimensionally, the components occupy a large area. Therefore, a pixel aperture ratio, that is, a ratio of a region through which light passes to the entire surface of the substrate may decrease. Therefore, in the conventional art, a method of forming the above-mentioned various components three-dimensionally. For example, a method of laminating the various components by interposing interlayer insulating layers is adopted. More specifically, the TFTs and the scanning lines, functioning as gate electrode films of the TFTs, are formed on the substrate. The data lines are formed on the TFTs and the scanning lines. The pixel electrodes are formed on the data lines. According to such a configuration, it is possible to enhance the pixel aperture ratio by appropriately arranging the various elements as well as to miniaturize the electro-optical device.
However, the related art electro-optical device has the following problems. According to the above-mentioned electro-optical device, the pixel electrodes and the data lines may be two-dimensionally or three-dimensionally formed to be close to each other in relatively narrow regions. However, in the above case, capacitance coupling may be generated between the pixel electrodes and the data lines. For example, once a voltage is applied, in a predetermined period, the potential of the pixel electrodes, which is supposed to be uniform, may change due to the conduction to the data lines close to the pixel electrodes. Therefore, stripe-shaped display irregularity along the data lines may be generated on an image.
Further, it matters that the life of the TFTs is relatively short. This is because positive charges are generated due to the diffusion of water molecules to the interface between the gate-insulating film and the semiconductor layer when moisture enters the semiconductor layer and the gate insulating film, which constitute the TFTs, thereby to increase a threshold voltage Vth in a relatively short period. Such a phenomenon is more appropriately applied to a P-channel TFT. As mentioned above, when the life of the TFTs is relatively short, the entire electro-optical device is affected and the quality of an image deteriorates at a relatively early stage. As a result, the electro-optical device itself may not operate.
Furthermore, in the above-mentioned laminated structure, in general, the pixel electrodes are formed in the uppermost layer and the TFTs are formed in the lowermost layer. Therefore, in order to electrically connect the pixel electrodes to the TFTs, another layer and a contact hole, which constitute the laminated structure, are interposed between the pixel electrodes and the TFTs. However, in such a case, for example, when it is desired to connect a transparent conductive material, such as ITO (indium tin oxide) which constitutes the pixel electrode to the above-mentioned layer, that is, an aluminum layer, electrolytic erosion occurs. Therefore, electric conduction between the transparent conductive material and the aluminum layer may deteriorate.